copy-files: Do not overwrite dos2unix with hd2u

Although hd2u is more powerful (as it e.g. can detect line endings without
changing them and reports mixed line endings) it has different semantics
and toggles line endings by default instead of forcing them to Unix. As
this can be misleading to the user, ship both tools.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>